The Maiar

[Findegil]

About Question I 5) I would like to add the following thought to Sarumanias very good answer: No Ainur (nor any fea of Erus children) could be extinguished by any means. The might to do that would only Eru have. And it would be as if you would try to force an idea you once had have to be as if never thought. If we are (as is Christian believe) build as lesser images of the Creator, then this special act would be very dificult even for an almighty God!

Anyhow, Tolkien makes it clear that in his sub-created world Ainur could not be extinguished.
That means Morgoth personally was cast out of Arda (probably also out of Ea), but that did not eliminate the Melkor content in Arda. The main problem of all these bad-guys was that by dominating their surrounding they distribute their own might, were by they reduce their personal being. Morgoth did that with the whole world ('Arda was Morgoth Ring'). Sauron with the Rings of Power and especially with the One Ring. With Saruman we are not that sure, but his trials in Ring-making are indications. Morgoth was removed as a person, but his sinister influence remained. Sauron was reduced personally to a ghost not able to make his hatred against the world effective. And the same seems to be true for Saruman.

Respectfully
Findegil